1. Field of the Invention
The present invention relates to a coil forming apparatus which forms coils to be mounted in slots of a stator core of a rotary electric machine from U-shaped conductor segments and a method of forming such coils.
2. Description of the Related Art
In a rotary electric machine such as a generator or a motor, a plurality of conductor segments is mounted into slots of a stator core to form a stator coil through a step of welding the respective ends of conductor segments in a well-known manner.
As shown in FIG. 11A, a hairpin-like conductor segment 100 having a U-turn portion and a pair of parallelly extending flat straight portions 120, 130 are preliminarily formed. Subsequently, the straight portions 120, 130 are twisted and pulled away from each other so that flat and wider surfaces become parallel to each other, as shown in FIG. 11B. Thereafter, the straight portions 120, 130 are inserted into a pair of slots of a stator core 310, as shown in FIG. 14.
U.S. Pat. No. 6,425,175 B1 discloses a pair of U-shaped conductor segments 100a, 100b, which are shown in FIG. 12 of this application and a twisting formation apparatus that twists a turn portion 110 of the conductor segments 100a, 100b, as shown in FIG. 13. The twisting formation apparatus has coaxially coupled inside ring 210 and an outside ring 220. Each of the rings 210, 220 has a plurality of circumferentially disposed holding slots whose cross-section is rectangular. The number of the holding slots of the inside and outside rings is the same as the number of slots of a stator core 310, which is shown in FIG. 14.
Although the above twisting formation apparatus is good for manufacturing a stator having four conductors each slot, it can not be applied to manufacturing a stator having six or more conductors each slot because the outermost turn portion of threefold U-shaped conductor segments excessively projects from a stator core, resulting in a stator having a very large axial size and a very heavy weight.